Does water flow type influence performances of reed based constructed wetland for wastewater treatment?

Abstract

The application of Phragmites australis based constructed wetlands (CW) have been widely used in various climates and also used for secondary treatment of diverse wastewater and polluted water. This work compares the treatment performance of two Phragmites-based mesocosms: the first with surface horizontal flow (SF), and the other with subsurface horizontal flow (SSF), in the same conditions of feeding and climate. The results showed a significantly high mineral content of the effluent water exiting SSF-CW. The last one was significantly more efficient in terms of removal of Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), Total Nitrogen (TN), ammonium (NH₄-N), and Total Phosphorus (TP) compared to SF-CW, i.e. 26.3, 3.12, 1.59, and 0.62 g. m^-2. day^-1 in the same order. The microbiological load reduction is also significantly higher in SSF-CW. On the contrary, the other parameters of pollution monitored do not allow the identification of a significant difference between SF- and SSF-CW. The atmospheric evapotranspiration value was higher in SSF-CW by 24.8 ± 20 mm. d^-1, corresponding also to a higher harvestable biomass of Phragmites of 58.2 t. ha^-1. year^-1.

Keywords: Biomass collecting; Evapotranspiration; Phragmites; Phytoremediation; Urban wastewater.